DFT Study of Adsorption of Lithium on Si, Ge-doped Divacancy Defected Graphene as Anode Material of Li-ion Battery

Graphene is an anode material that is expected to be a good alternative for graphite to increase the capacity and rate-capability of lithium-ion batteries. Graphene synthesis is always accompanied by defects in the structure. The most common defect in graphene is the divacancy (DV) defect. In this study, the effect of this defect on the adsorption of lithium was studied by density functional theory method, and also the doping effect of silicon and germanium atoms on the defective graphene structure was investigated. The bandgap energy of DV-defected graphene, which has an inverse relationship with electrical conductivity, is steady with the addition of germanium, but decreases with the addition of silicon. In all cases, along with lithium adsorption, the bandgap energy is increased, so that the germanium doped compound has the highest bandgap and the structure with no doped atom has the least bandgap. However, the difference in the minimum and maximum bandgap in structures is very low. The results show that the addition of silicon and germanium leads to stronger adsorption of lithium which means it is possible to raise the charge-discharge capacity of graphene through doping with elements while the material still has a high charge/discharge capability.